Solar cells are typically photovoltaic (PV) devices that convert sunlight directly into electricity. PV cells typically include a semiconductor (e.g., silicon) that absorbs light irradiation (e.g., sunlight) in a way that creates free electrons, which in turn are caused to flow in the presence of a built-in field to create direct current (DC) power. The DC power generated by several PV cells may be collected on a grid placed on the cell. Current from multiple PV cells is then combined by series and parallel combinations into higher currents and voltages. The DC power thus collected may then be sent over wires, often many dozens or even hundreds of wires.
The DC power generated by solar cells is suitable for small-scale DC systems, such as solar powered calculators or remote sensors, but presents several problems when utilized on a larger scale, such as in homes and businesses.
A first problem associated with the large-scale use of solar power is that the DC power must first be converted using an expensive power inverter into a suitable alternating current (AC) signal before it can be used to power common household appliances, or transformed to high voltage for transmission over the power grid. Over a century ago, Nicola Tesla and Thomas Edison battled each other on the merits of AC versus DC for power transmission. Edison fought stubbornly and lost. AC power became recognized as the superior form of electricity for power distribution for several important reasons, including cost, reliability, and efficiency. As a result, household appliances that utilize distributed power (i.e., by way of a plug that is inserted into a wall socket) are configured to run on AC power. Because solar cells generate DC power, this DC power must first be converted into the AC power required to run the appliances. Currently, this DC-to-AC power conversion requires the use of a power converter, which is an expensive device that makes up a significant portion of the total cost of generating AC power using solar energy.
The high DC-to-AC conversion expense may be avoided by utilizing solar cells in large DC systems, but this approach generates several expensive obstacles as well. First, large scale DC power use causes corrosion or electro-migration under some conditions that stems from the high DC currents, and current capacity limitations are imposed by these DC currents that increase system cost. Even if these technical problems can be solved, the conversion to DC power would require the wholesale replacement of conventional AC appliances with a new line of DC powered appliances. Due to these issues, although there have been pilot projects to wire buildings with separate DC power systems to specifically accommodate solar installations, it is unlikely that there will be broad adoption of this approach as long as solar cells generate DC power.
What is needed is a solar power apparatus that generates AC power without the need for power inverters.